The invention relates to a CATV terminal unit and, more particularly, to a two-way CATV terminal unit for providing effective means to detect when the subscriber or a third party opens the terminal unit cover to possibly alter its interior mechanism.
Most conventionally used CATV systems have been of a one-way type in which a center unilaterally transmits a plurality of television programs through a number of channels and the subscriber can view the program by operating a converter to convert each channel to a vacant channel (a channel having no television broadcasting) of his television receiver. In this case, however, it is very difficult to record what program has been viewed and how long a subscriber has viewed the program and therefore the system manager has been obliged to uniformly charge the subscribers on a periodic usage basis. In order to provide expensive programs, such as films that are high in production cost or newly released, to specified subscribers only, a system has been also used in which the subscriber an view the special program by inserting into the converter (terminal unit) a key or a specially processed card which is hired or sold. However, this system is troublesome for both the system manager and the subscriber.
The apparatus for detecting removal of the CATV terminal unit cover in accordance with the present invention is premised on an assumption that the apparatus is used with a new system free from the disadvantages found in the conventional CATV system. The new system referred herein is generally such that its head end is connected through two-way transmission paths to tens of thousands of terminal units each numbered differently from one to another and is associated with a computer for sequentially calling up the respective terminal units (this operation is herein referred to as polling) and for collecting coded data signals indicating the respective terminal unit states such as which channel is viewed. A system having its head end capable of determining the status of the respective terminal units at frequent intervals permits making a charge to the subscriber for every channel and for every program viewed. Furthermore, in the case where keys are lent to specified subscribers in order to prevent general subscribers or minors from viewing a certain channel, such a system can detect in polling (1) whether or not the terminal unit is owned by the subscriber having the key, (2) whether or not the key is inserted into the converter, and (3) whether or not the subscriber views the special program requiring the key. This is very convenient for system management. However, the system also involves difficult problems such that where a person removes the terminal unit cover from the terminal unit and alters its interior mechanism without permission, that person can view the special program and the head end cannot establish a correct account of the charge to him.
Therefore, the present invention has for its object to provide a satisfactory solution of the above mentioned problems.
It is another object of the present invention to provide a terminal unit for CATV systems which can inform the head end whenever the subscriber or third party opens the terminal unit cover.
It is still another object of the present invention to provide a cover removal detecting apparatus for CATV terminal units which is easy to manufacture.
It is still another object of the present invention to provide a cover removal detecting apparatus for CATV terminal units in which as soon as the person takes a screw bolt off a screw hole to open the unit cover, the scre whole is closed to prevent the screw bolt from being screwed into the screw hole again and at the same time this condition is informed to the head end.
It is still another object of the present invention to provide a cover removal detecting apparatus for CATV terminal units in which after the cover is removed once from the terminal unit, it is difficult for members of the general public to set the cover to its initial condition and it is easy for service men to do so.